Stonehenge Subwoofer Flat Pack Assembly

Building this subwoofer is actually a lot easier than my instructions might sound and can be done in a day with very little effort. I'm just trying to give as much detail as I can so you should read through all of this prior to starting. The kit itself will go together okay even if you have some slight assembly errors with bracing or side panels not being 100% squared up. That's always a goal for my flat pack designs. If you see any mistakes in my instructions, please let me know.


The rear panel has all the letters carved into the back so you can see where all of the inner panels go. They're hard to see in the first picture because of the lighting.

 

The first step is to make sure there isn't any MDF dust inside any of the grooves before you glue the braces or panels in. I do go over each one after they come back from the CNC company, but it makes sense to double check either way.


Also, make sure you dry fit every piece and double check where you will need wood glue on each panel. Anywhere wood touches you want glue. After gluing and clamping you can remove the clamps in about 30 minutes as long as you don't plan on stressing the joints. There's really no need to let each piece dry overnight.



The first braces to glue down are the cross braces. Clamping these down isn't 100% needed. But you can lay a 36" long scrap board across them and then clamp down the edges of that scrap piece of wood. That would hold the crossbraces tighter to the rear panel. Or you could lay a weight directly on them. I also wipe a little glue where the 2 braces slide together just to be sure.

 

The next step is to start gluing in the internal braces. You don't need a lot of glue for these and it doesn't really matter which ones you start with first. On mine, I started with the four outer braces. These are easy to clamp down if the entire project is sitting up on a couple 2x4's, or even the corner protectors that come with your kit. Make sure your brace is lined up with the rabbet joints where the side panels go.

 

I then started with the 'Stonehenge' style braces. The first ones in are the ones that push up against the cross braces. Make sure you also put glue where they touch the cross brace. You can lightly clamp 2 opposing braces together at the same time with one clamp if you wanted to. There's no need for a lot of clamping pressure here at all. Just make sure the braces are standing up fairly straight (they don't have to be 100% perfect). You could probably lay a board across the top of a few braces and put a little weight on it if you were worried about them shifting while they dry. I didn't, but you might want to just to make sure all the bracing is close to the same height.







I then added the remaining Stonehenge braces.

 

The next step is to install the inner port panels marked 'A' and 'B'. Dry fit them into the grooves that are cut on the rear panel so you can see how they are suppose to fit together. I installed these 2 panels one right after the other to make sure everything lined up properly, but you could do one at a time once you see how they fit together. There should be glue anywhere 2 pieces of wood touch. Lightly clamp the 2 panels together where they meet at 90 degrees. Again, you could lay a board on top of all these pieces and add weight to hold them down into the rear panel.

 

Believe it or not the hardest part of the assembly is now done.


Next you want to glue up side panel 'C'. Be sure to dry fit the panel in place to see where you need wood glue to be. Don't forget to put glue where the side panel meets the internal braces. I used small 6" clamps to hold the side panel to the inner braces so it doesn't move. I then used 18" clamps to pull the side panel down onto the rear panel.


After about 30-60 minutes, you can remove the clamps and do the same thing for the top panel 'D'.


This is what you should now have:

 

You probably noticed 2 small square blocks of wood in your kit and wondered where they go. These are optional braces for the inside of the port. They aren't really needed, but I thought some people might want them. You can glue them anywhere inside the ports that you want, but I would shoot for somewhere around the middle of panel 'E' and 'F'.


You can see where they go with the following badly lit picture:









The blocks can be glued directly to panels 'E' and 'F' before you install the panels Pay attention that you are putting them length wise. i would dry fit the panel before gluing and see how the small blocks need to be situated.


Here are photos showing how I would do it:


Glue one block to Panel 'E' and let it dry 30 minutes before installing the panel:







Glue the other block to panel 'F' and let it dry 30 minutes before installing the panel:

 

After those small blocks are glued onto your panels and dry enough, go ahead and install panel 'E' and 'F' just like you did the previous two outer panels. If you used the small blocks, make sure you put glue on the top of them where they will be touching the inner panel.

You're almost done. This is what you should currently have:







It wouldn't hurt to look around and make sure all the panels are sealed up okay. The wood glue likely sealed everything up just fine and I've never had to add any caulking in the corners.

 

The final step is to glue the front baffle onto your box. Before adding any glue, lay the baffle on your box and make sure it's lining up okay. If you glued any panels up a little bit crooked, just spin or flip the baffle around until it lines up with the edges of your box as nice as possible. Chances are, after your box is 100% glued up and done, you will need to do some light sanding around the edges anyway. That's perfectly normal. Just try to get the baffle glued on as close to square as you can.

You will need to put wood glue on the top of every brace and on top of all the other panels, including the panels that make up the inner port. Having a friend help you align the baffle on top might help, but I was able to lay it on myself okay.

Clamping the top on can be tedious as things slide around, but don't get too worried, you'll get it. A couple clamps on opposing sides will hold it in place. Just lightly tighten them all down a little bit each time and just work your way around the box. There's no need to overtighten the clamps. The glue bond is actually stronger than the wood, so there's no reason to try and squeeze out all the glue you just used. Once you have a few clamps tightened enough to keep the baffle from sliding around, go ahead and add more clamps around the perimeter as you see fit.

Another trick is to lay a 36" thick board or metal beam across the top of the box and clamp down each side of the board. This will evenly distribute pressure across the top of your box.

Guess what? You're done!

 

What makes the 'Stonehenge' bracing so unique isn't just how easy it assembles. Every screw used to hold your woofer in place will go into it's own internal brace that mechanically locks it to the front panel and all the way through to the rear panel! There is no other bracing system quite like it.

If you need to add a plate amp, you can easily install it directly behind the woofer where the cross braces are. This will not weaken the box at all because you are removing wood and replacing it with the amp's aluminum mounting plate, which is actually stronger than the mdf you removed.

Ported subwoofers don't need as much stuffing as sealed ones. Most people just line the inner walls with poly batting, or acoustic foam. Some people don't use any stuffing or lining at all.